Py-GCMS studies of Indian coals and their solvent extracted products

Five Indian coals having different characteristics, i.e., coking, rank, grade, and carbon and volatile matter (VM) content, were subjected to solvent extraction under mild, ambient pressure conditions to obtain almost ash-free coals. N-methyl pyrrolidone (NMP) containing a small amount of ethylenediamine (EDA) was used as the solvent, the resulting super clean coal (SCC) products being characterised by means of ultimate analysis, solid-state ¹³C NMR spectroscopy, thermogravimetric analysis (TGA) and pyrolysis-GCMS. The super clean products were found to have increased volatile matter content because of the removal of disassociations and entanglements and the disruption of intermolecular forces. Based on comparison of the pyrolysis-GCMS data for the original (raw) coals (OCs) and SCCs, the extraction led to the segregation of the coal samples into easily volatilized components and strongly cross-linked networks of polycyclic fused ring aromatic components. The polycondensed aromatic components were present in higher concentration in the super clean coals, demonstrating the selectivity of the solvents to act upon the condensed aromatic components and long chain alkanes and extract them selectively, thereby resulting in a more aromatic product.